Semiconductor substrate (“substrate”) fabrication often includes exposing a substrate to a plasma to allow the reactive constituents of the plasma to modify the surface of the substrate, e.g., remove material from unprotected areas of the substrate surface. The substrate characteristics resulting from the plasma fabrication process are dependent on the process conditions, including the plasma characteristics and substrate temperature. For example, in some plasma processes a critical dimension, i.e., feature width, on the substrate surface can vary by about one nanometer per ° C. of substrate temperature. It should be appreciated that differences in substrate temperature between otherwise identical substrate fabrication processes will result in different substrate surface characteristics. Thus, a drift in process results between different substrates can be caused by variations in substrate temperature during plasma processing. Additionally, center-to-edge substrate temperature variations can adversely affect a die yield per substrate.
A general objective in substrate fabrication is to optimize a die yield per substrate and fabricate each substrate of a common type in as identical a manner as possible. To meet these objectives, it is necessary to control fabrication parameters that influence the plasma processing characteristics across an individual substrate and among various substrates of a common type. Because plasma constituent reactivity is proportional to temperature, substrate temperature and plasma exposed surface temperatures can have a strong influence on plasma processing results across the substrate and among various substrates. Therefore, a continuing need exists for improvements in temperature control during plasma fabrication processes.